/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.banciyuan.bcywebview.utils.http;

import android.os.SystemClock;

import com.android.volley.Cache;
import com.android.volley.VolleyLog;

import java.io.EOFException;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.concurrent.Callable;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask;
import java.util.concurrent.PriorityBlockingQueue;
import java.util.concurrent.RunnableFuture;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;

/**
 * Cache implementation that caches files directly onto the hard disk in the specified
 * directory. The default disk usage size is 5MB, but is configurable.
 * <pre>
 * <b>NOTE</b>
 * This is a new version of {@code DiskBasedCache} which is fixed the performance issue where initialize() works too slow if there is a much of cache entries.
 * See below if you want to know the issue in detail.
 * http://stackoverflow.com/questions/20916478/performance-issue-with-volleys-diskbasedcache
 *
 * This class came from the commit, https://android.googlesource.com/platform/frameworks/volley/+/11089542825c9575f90341670ef08762579bc2b0 .
 * And the author was Anders Aagaard.
 *
 * After the issue is resolved in master branch of aosp volley, this class will be deprecated.
 * </pre>
 */
public class DiskBasedCache implements Cache {

    /**
     * Number of threads to use when loading cache from disk
     */
    private final int CACHE_LOAD_THREADS = 2;

    /**
     * Map of the Key, CacheHeader pairs
     */
    private final CacheContainer mEntries = new CacheContainer();

    /**
     * The root directory to use for the cache.
     */
    private final File mRootDirectory;

    /**
     * The maximum size of the cache in bytes.
     */
    private final int mMaxCacheSizeInBytes;

    /**
     * Default maximum disk usage in bytes.
     */
    private static final int DEFAULT_DISK_USAGE_BYTES = 5 * 1024 * 1024;

    /**
     * High water mark percentage for the cache
     */
    private static final float HYSTERESIS_FACTOR = 0.9f;

    /**
     * Magic number for current version of cache file format.
     */
    private static final int CACHE_MAGIC = 0x20140623;

    /**
     * Constructs an instance of the DiskBasedCache at the specified directory.
     *
     * @param rootDirectory       The root directory of the cache.
     * @param maxCacheSizeInBytes The maximum size of the cache in bytes.
     */
    public DiskBasedCache(File rootDirectory, int maxCacheSizeInBytes) {
        mRootDirectory = rootDirectory;
        mMaxCacheSizeInBytes = maxCacheSizeInBytes;
    }

    /**
     * Constructs an instance of the DiskBasedCache at the specified directory using
     * the default maximum cache size of 5MB.
     *
     * @param rootDirectory The root directory of the cache.
     */
    public DiskBasedCache(File rootDirectory) {
        this(rootDirectory, DEFAULT_DISK_USAGE_BYTES);
    }

    /**
     * Clears the cache. Deletes all cached files from disk.
     */
    @Override
    public synchronized void clear() {
        File[] files = mRootDirectory.listFiles();
        if (files != null) {
            for (File file : files) {
                file.delete();
            }
        }
        mEntries.clear();
        VolleyLog.d("Cache cleared.");
    }

    /**
     * Returns the cache entry with the specified key if it exists, null otherwise.
     */
    @Override
    public synchronized Entry get(String key) {
        CacheHeader entry = mEntries.get(key);
        // if the entry does not exist, return.
        if (entry == null) {
            return null;
        }

        File file = getFileForKey(key);
        CountingInputStream cis = null;
        try {
            cis = new CountingInputStream(new FileInputStream(file));
            CacheHeader.readHeader(cis); // eat header
            byte[] data = streamToBytes(cis, (int) (file.length() - cis.bytesRead));
            return entry.toCacheEntry(data);
        } catch (Exception e) {
            VolleyLog.d("%s: %s", file.getAbsolutePath(), e.toString());
            remove(key);
            return null;
        } finally {
            if (cis != null) {
                try {
                    cis.close();
                } catch (IOException ioe) {
                    return null;
                }
            }
        }
    }

    /**
     * Initializes the DiskBasedCache by scanning for all files currently in the
     * specified root directory. Creates the root directory if necessary.
     */
    @Override
    public synchronized void initialize() {
        mEntries.initialize();
    }

    /**
     * Invalidates an entry in the cache.
     *
     * @param key        Cache key
     * @param fullExpire True to fully expire the entry, false to soft expire
     */
    @Override
    public synchronized void invalidate(String key, boolean fullExpire) {
        Entry entry = get(key);
        if (entry != null) {
            entry.softTtl = 0;
            if (fullExpire) {
                entry.ttl = 0;
            }
            put(key, entry);
        }

    }

    /**
     * Puts the entry with the specified key into the cache.
     */
    @Override
    public synchronized void put(String key, Entry entry) {
        pruneIfNeeded(entry.data.length);
        File file = getFileForKey(key);
        try {
            FileOutputStream fos = new FileOutputStream(file);
            CacheHeader e = new CacheHeader(key, entry);
            boolean success = e.writeHeader(fos);
            if (!success) {
                fos.close();
                VolleyLog.d("Failed to write header for %s", file.getAbsolutePath());
                throw new IOException();
            }
            fos.write(entry.data);
            fos.close();
            putEntry(key, e);
            return;
        } catch (IOException e) {
        }
        boolean deleted = file.delete();
        if (!deleted) {
            VolleyLog.d("Could not clean up file %s", file.getAbsolutePath());
        }
    }

    /**
     * Removes the specified key from the cache if it exists.
     */
    @Override
    public synchronized void remove(String key) {
        boolean deleted = getFileForKey(key).delete();
        removeEntry(key);
        if (!deleted) {
            VolleyLog.d("Could not delete cache entry for key=%s, filename=%s",
                    key, getFilenameForKey(key));
        }
    }

    /**
     * Creates a pseudo-unique filename for the specified cache key.
     *
     * @param key The key to generate a file name for.
     * @return A pseudo-unique filename.
     */
    private String getFilenameForKey(String key) {
        int firstHalfLength = key.length() / 2;
        String localFilename = String.valueOf(key.substring(0, firstHalfLength).hashCode());
        localFilename += String.valueOf(key.substring(firstHalfLength).hashCode());
        return localFilename;
    }

    /**
     * Returns a file object for the given cache key.
     */
    public File getFileForKey(String key) {
        return new File(mRootDirectory, getFilenameForKey(key));
    }

    /**
     * Prunes the cache to fit the amount of bytes specified.
     *
     * @param neededSpace The amount of bytes we are trying to fit into the cache.
     */
    private void pruneIfNeeded(int neededSpace) {
        if (!mEntries.isLoaded()) {
            // the lru cache can go slightly above neededSpace if putting entries during cache initialization
            return;
        }
        if ((mEntries.getTotalSize() + neededSpace) < mMaxCacheSizeInBytes) {
            return;
        }
        if (VolleyLog.DEBUG) {
            VolleyLog.v("Pruning old cache entries.");
        }

        long before = mEntries.getTotalSize();
        int prunedFiles = 0;
        long startTime = SystemClock.elapsedRealtime();

        Iterator<Map.Entry<String, CacheHeader>> iterator = mEntries.entrySet().iterator();
        while (iterator.hasNext()) {
            Map.Entry<String, CacheHeader> entry = iterator.next();
            CacheHeader e = entry.getValue();
            boolean deleted = getFileForKey(e.key).delete();
            if (!deleted) {
                VolleyLog.d("Could not delete cache entry for key=%s, filename=%s",
                        e.key, getFilenameForKey(e.key));
            }
            iterator.remove();
            prunedFiles++;

            if ((mEntries.getTotalSize() + neededSpace) < mMaxCacheSizeInBytes * HYSTERESIS_FACTOR) {
                break;
            }
        }

        if (VolleyLog.DEBUG) {
            VolleyLog.v("pruned %d files, %d bytes, %d ms",
                    prunedFiles, (mEntries.getTotalSize() - before), SystemClock.elapsedRealtime() - startTime);
        }
    }

    /**
     * Puts the entry with the specified key into the cache.
     *
     * @param key   The key to identify the entry by.
     * @param entry The entry to cache.
     */
    private void putEntry(String key, CacheHeader entry) {
        mEntries.put(key, entry);
    }

    /**
     * Removes the entry identified by 'key' from the cache.
     */
    private void removeEntry(String key) {
        CacheHeader entry = mEntries.get(key);
        if (entry != null) {
            mEntries.remove(key);
        }
    }

    /**
     * Reads the contents of an InputStream into a byte[].
     */
    private static byte[] streamToBytes(InputStream in, int length) throws Exception {
        byte[] bytes = new byte[length];
        int count;
        int pos = 0;
        while (pos < length && ((count = in.read(bytes, pos, length - pos)) != -1)) {
            pos += count;
        }
        if (pos != length) {
            throw new IOException("Expected " + length + " bytes, read " + pos + " bytes");
        }
        return bytes;
    }

    /**
     * Container for CacheHeader, both before and after loading them into memory.
     */
    private class CacheContainer extends ConcurrentHashMap<String, CacheHeader> {
        private final PriorityBlockingQueue<Runnable> mQueue = new PriorityBlockingQueue<Runnable>();
        private final Map<String, Future<CacheHeader>> mLoadingFiles =
                new ConcurrentHashMap<String, Future<CacheHeader>>();

        /**
         * Total amount of space currently used by the cache in bytes.
         */
        private AtomicLong mTotalSize = new AtomicLong(0);

        /**
         * Whether or not cache initialization has been started
         */
        private boolean mInitialized = false;

        public CacheContainer() {
            super(16, .75f, CACHE_LOAD_THREADS);
        }


        /**
         * Initializes the DiskBasedCache by scanning for all files currently in the
         * specified root directory. Creates the root directory if necessary.
         */
        public synchronized void initialize() {
            if (mInitialized) {
                return;
            }
            mInitialized = true;
            if (!mRootDirectory.exists()) {
                if (!mRootDirectory.mkdirs()) {
                    VolleyLog.e("Unable to create cache dir %s", mRootDirectory.getAbsolutePath());
                }
                return;
            }

            File[] files = mRootDirectory.listFiles();
            if (files == null) {
                return;
            }
            VolleyLog.d("Loading %d files from cache", files.length);

            ExecutorService executor = new ThreadPoolExecutor(CACHE_LOAD_THREADS, CACHE_LOAD_THREADS,
                    10, TimeUnit.MILLISECONDS, mQueue);
            for (File file : files) {
                Callable<CacheHeader> callable = new HeaderParserCallable(file);
                RunnableFuture<CacheHeader> submit = new ReorderingFutureTask(callable);
                mLoadingFiles.put(file.getName(), submit);
                executor.execute(submit);
            }
        }

        /**
         * A task that reorders itself to the top of the queue if a thread requests access to it
         */
        private class ReorderingFutureTask extends FutureTask<CacheHeader>
                implements Comparable<ReorderingFutureTask> {
            private int mGetRequests = 0;

            public ReorderingFutureTask(Callable<CacheHeader> callable) {
                super(callable);
            }

            @Override
            public CacheHeader get() throws InterruptedException, ExecutionException {
                mGetRequests++;
                if (mQueue.contains(this)) {
                    mQueue.remove(this);
                    mQueue.add(this);
                }
                return super.get();
            }

            @Override
            public int compareTo(ReorderingFutureTask another) {
                return mGetRequests > another.mGetRequests
                        ? -1 : mGetRequests < another.mGetRequests ? +1 : 0;
            }
        }

        /**
         * A callable that parses CacheHeader and returns a valid cache entry.
         */
        private class HeaderParserCallable implements Callable<CacheHeader> {
            private final File file;

            public HeaderParserCallable(File file) {
                this.file = file;
            }

            @Override
            public CacheHeader call() throws Exception {
                FileInputStream fis = null;
                try {
                    fis = new FileInputStream(file);
                    CacheHeader entry = CacheHeader.readHeader(fis);
                    entry.size = file.length();
                    CacheContainer.super.put(entry.key, entry);
                    mTotalSize.getAndAdd(entry.size);
                    return entry;
                } catch (IOException e) {
                    if (file != null) {
                        file.delete();
                    }
                } finally {
                    try {
                        if (fis != null) {
                            fis.close();
                        }
                    } catch (IOException ignored) {
                    }
                    mLoadingFiles.remove(file.getName());
                }
                return null;
            }
        }

        /**
         * Waits until the cache is ready and loaded
         */
        private void waitForCache() {
            while (mLoadingFiles.size() > 0) {
                Iterator<Map.Entry<String, Future<CacheHeader>>> iterator =
                        mLoadingFiles.entrySet().iterator();
                if (iterator.hasNext()) {
                    Map.Entry<String, Future<CacheHeader>> entry = iterator.next();
                    try {
                        entry.getValue().get();
                    } catch (InterruptedException ignored) {
                    } catch (ExecutionException ignored) {
                    }
                }
            }
        }

        /**
         * Waits until the specified cache key is ready and loaded.
         */
        private void waitForKey(Object key) {
            if (isLoaded()) {
                return;
            }
            String filename = getFilenameForKey((String) key);
            Future<CacheHeader> future = mLoadingFiles.get(filename);
            if (future != null) {
                try {
                    future.get();
                } catch (InterruptedException ignored) {
                } catch (ExecutionException ignored) {
                }
            }
        }

        /**
         * Returns true if the cache is 100% loaded.
         */
        public boolean isLoaded() {
            return mLoadingFiles.size() == 0;
        }

        /**
         * Returns the total size of the cache
         */
        public long getTotalSize() {
            return mTotalSize.get();
        }

        /**
         * Gets an entry from the cache
         *
         * @param key The key to identify the entry by.
         */
        @Override
        public CacheHeader get(Object key) {
            waitForKey(key);
            return super.get(key);
        }

        /**
         * Checks if an entry exists in the cache and returns true/false accordingly.
         *
         * @param key The key to identify the entry by.
         */
        @Override
        public boolean containsKey(Object key) {
            waitForKey(key);
            return super.containsKey(key);
        }

        /**
         * Puts the entry with the specified key into the cache without waiting for cache key.
         *
         * @param key   The key to identify the entry by.
         * @param entry The entry to cache.
         */
        @Override
        public CacheHeader put(String key, CacheHeader entry) {
            waitForKey(key);
            if (super.containsKey(key)) {
                mTotalSize.getAndAdd(entry.size - super.get(key).size);
            } else {
                mTotalSize.getAndAdd(entry.size);
            }
            return super.put(key, entry);
        }

        /**
         * Remove an entry from the cache
         *
         * @param key The key to identify the entry by.
         */
        @Override
        public CacheHeader remove(Object key) {
            waitForKey(key);
            if (super.containsKey(key)) {
                mTotalSize.getAndAdd(-1 * super.get(key).size);
            }
            return super.remove(key);
        }

        /**
         * Clears the cache
         */
        @Override
        public void clear() {
            waitForCache();
            mTotalSize.getAndSet(0);
            super.clear();
        }
    }

    /**
     * Handles holding onto the cache headers for an entry.
     */
    // Visible for testing.
    static class CacheHeader {
        /**
         * The size of the data identified by this CacheHeader. (This is not
         * serialized to disk.
         */
        public long size;

        /**
         * The key that identifies the cache entry.
         */
        public String key;

        /**
         * ETag for cache coherence.
         */
        public String etag;

        /**
         * Date of this response as reported by the server.
         */
        public long serverDate;

        /**
         * TTL for this record.
         */
        public long ttl;

        /**
         * Soft TTL for this record.
         */
        public long softTtl;

        /**
         * Headers from the response resulting in this cache entry.
         */
        public Map<String, String> responseHeaders;

        private CacheHeader() {
        }

        /**
         * Instantiates a new CacheHeader object
         *
         * @param key   The key that identifies the cache entry
         * @param entry The cache entry.
         */
        public CacheHeader(String key, Entry entry) {
            this.key = key;
            this.size = entry.data.length;
            this.etag = entry.etag;
            this.serverDate = entry.serverDate;
            this.ttl = entry.ttl;
            this.softTtl = entry.softTtl;
            this.responseHeaders = entry.responseHeaders;
        }

        /**
         * Reads the header off of an InputStream and returns a CacheHeader object.
         *
         * @param is The InputStream to read from.
         * @throws IOException
         */
        public static CacheHeader readHeader(InputStream is) throws Exception {
            CacheHeader entry = new CacheHeader();
            int magic = readInt(is);
            if (magic != CACHE_MAGIC) {
                // don't bother deleting, it'll get pruned eventually
                throw new IOException();
            }
            entry.key = readString(is);
            entry.etag = readString(is);
            if (entry.etag.equals("")) {
                entry.etag = null;
            }
            entry.serverDate = readLong(is);
            entry.ttl = readLong(is);
            entry.softTtl = readLong(is);
            entry.responseHeaders = readStringStringMap(is);
            return entry;
        }

        /**
         * Creates a cache entry for the specified data.
         */
        public Entry toCacheEntry(byte[] data) {
            Entry e = new Entry();
            e.data = data;
            e.etag = etag;
            e.serverDate = serverDate;
            e.ttl = ttl;
            e.softTtl = softTtl;
            e.responseHeaders = responseHeaders;
            return e;
        }


        /**
         * Writes the contents of this CacheHeader to the specified OutputStream.
         */
        public boolean writeHeader(OutputStream os) {
            try {
                writeInt(os, CACHE_MAGIC);
                writeString(os, key);
                writeString(os, etag == null ? "" : etag);
                writeLong(os, serverDate);
                writeLong(os, ttl);
                writeLong(os, softTtl);
                writeStringStringMap(responseHeaders, os);
                os.flush();
                return true;
            } catch (IOException e) {
                VolleyLog.d("%s", e.toString());
                return false;
            }
        }

    }

    private static class CountingInputStream extends FilterInputStream {
        private int bytesRead = 0;

        private CountingInputStream(InputStream in) {
            super(in);
        }

        @Override
        public int read() throws IOException {
            int result = super.read();
            if (result != -1) {
                bytesRead++;
            }
            return result;
        }

        @Override
        public int read(byte[] buffer, int offset, int count) throws IOException {
            int result = super.read(buffer, offset, count);
            if (result != -1) {
                bytesRead += result;
            }
            return result;
        }
    }

    /*
     * Homebrewed simple serialization system used for reading and writing cache
     * headers on disk. Once upon a time, this used the standard Java
     * Object{Input,Output}Stream, but the default implementation relies heavily
     * on reflection (even for standard types) and generates a ton of garbage.
     */

    /**
     * Simple wrapper around {@link InputStream#read()} that throws EOFException
     * instead of returning -1.
     */
    private static int read(InputStream is) throws IOException {
        int b = is.read();
        if (b == -1) {
            throw new EOFException();
        }
        return b;
    }

    static void writeInt(OutputStream os, int n) throws IOException {
        os.write((n >> 0) & 0xff);
        os.write((n >> 8) & 0xff);
        os.write((n >> 16) & 0xff);
        os.write((n >> 24) & 0xff);
    }

    static int readInt(InputStream is) throws IOException {
        int n = 0;
        n |= (read(is) << 0);
        n |= (read(is) << 8);
        n |= (read(is) << 16);
        n |= (read(is) << 24);
        return n;
    }

    static void writeLong(OutputStream os, long n) throws IOException {
        os.write((byte) (n >>> 0));
        os.write((byte) (n >>> 8));
        os.write((byte) (n >>> 16));
        os.write((byte) (n >>> 24));
        os.write((byte) (n >>> 32));
        os.write((byte) (n >>> 40));
        os.write((byte) (n >>> 48));
        os.write((byte) (n >>> 56));
    }

    static long readLong(InputStream is) throws IOException {
        long n = 0;
        n |= ((read(is) & 0xFFL) << 0);
        n |= ((read(is) & 0xFFL) << 8);
        n |= ((read(is) & 0xFFL) << 16);
        n |= ((read(is) & 0xFFL) << 24);
        n |= ((read(is) & 0xFFL) << 32);
        n |= ((read(is) & 0xFFL) << 40);
        n |= ((read(is) & 0xFFL) << 48);
        n |= ((read(is) & 0xFFL) << 56);
        return n;
    }

    static void writeString(OutputStream os, String s) throws IOException {
        byte[] b = s.getBytes("UTF-8");
        writeLong(os, b.length);
        os.write(b, 0, b.length);
    }

    static String readString(InputStream is) throws Exception {
        int n = (int) readLong(is);
        byte[] b = streamToBytes(is, n);
        return new String(b, "UTF-8");
    }

    static void writeStringStringMap(Map<String, String> map, OutputStream os) throws IOException {
        if (map != null) {
            writeInt(os, map.size());
            for (Map.Entry<String, String> entry : map.entrySet()) {
                writeString(os, entry.getKey());
                writeString(os, entry.getValue());
            }
        } else {
            writeInt(os, 0);
        }
    }

    static Map<String, String> readStringStringMap(InputStream is) throws Exception {
        int size = readInt(is);
        Map<String, String> result = (size == 0)
                ? Collections.<String, String>emptyMap()
                : new HashMap<String, String>(size);
        for (int i = 0; i < size; i++) {
            String key = readString(is).intern();
            String value = readString(is).intern();
            result.put(key, value);
        }
        return result;
    }


}